Cathodes for electrical discharge devices



Sept. 4D 1956 H. KA-rz ETAL cmi-longs FOR ELECTRICAL DISCHARGE DEVICES Filed June 9. 1952 United States Patent O CATHODES FOR ELECTRICAL DISCHARGE DEVICES Helmut Katz and Karl Ludwig Rau, Erlangen, Germany, assiguors to Siemens & Halske Aktiengesellschaft, Munich and Berlin, Germany, a German corporation Application June 9, 1952, Serial No. 292,432 Claims priority, application Germany June `9, 1951 s claims. (ci. 313-337) This invention relates to cathodes for use in electrical discharge devices, especially to cathodes having a supply of emissive material which migrates at operating temperature through pores or line passages of the cathode body to the emitting surface thereof, and is particularly concerned with cathodes having a heating system which permits individual control or dosing of the heat transmitted to the emissive material and to the body forming the emitting surface, respectively.

The fine pasasges for the migration of the emissive material may be formed by wires or striplike bands wound on the emitting cathode, or by a sintered-body forming the cathode surface and having a porous structure and being of a material which permits migration of the emissive material. Tungsten or molybdenum is in the latter case particularly suitable when using thorium or barium compositions as emissive materials.

. The cathode must provide for optimal coverage or spreading of the emissive material upon the emitting surface at the operating temperature applied. If the reduction or vaporization velocity of the barium or thorium composition does not have the proper value at such temperature, there will not be optimal coverage or spreading of the emissive material on the cathode surface and it will consequently be necessary to increase the temperature so as to obtain proper emission. If the reduction or vaporization velocity is too great, there willbe produced a wasteful excess of the emissive material, and the life of the cathode will be shortened. Waste and inecient operation will be the result in either case.

The invention avoids these drawbacks by the provision of a heating system which permits individual control or dosing of the heat transmitted to the emissive material and to the body forming the emission surface of the cathode, respectively, so as to obtain diierentiated heating thereof, for the purpose of providing for the continuous liberation of the proper amounts of emissive material and migration thereof to the emitting surface to produce optimal spreading or coverage of such material thereon and consequently continuous optimal specific emission.

The heating system according to the invention may comprise two separate heaters, one for affecting primarily the emissive material and the other for affecting primarily the body forming the emitting surface. The current supply to the two heaters may be individually and independently adjustable. This may be done by any known and suitable means for regulating the current supply to the heaters. It is therefore immaterial whether the heating is direct or indirect. It may be of advantage in some cases to provide one or both heaters for direct heating.

A commen heater may, however, be provided, and the emissive material as well as the body forming the emission surface may be suitably geometrically disposed with respect to the common heater so that the above-mentioned differentiated heat transfer or distribution will result. Suitable means, for example, a suitable dielectric, may for this purpose be disposed in the path of the heat transfer from the common heater to provide for the differentiating ICC heat transfer to the emissive material and to the body forming the emission surface, respectively. The emissive material and the body forming the emission surface may also be differentially spaced from the heater so as to effect the differentiated heat transfer thereto.

The invention will now be explained with reference to the accompanying drawings showing various embodiments.

In the drawings,

Figs. l, 4 and 5 show tubular cathodes; and

Figs. 2 and 3 indicate cathodes forming dat emitting surfaces.

In the embodiment according to Fig. l there is provided a single heater in the form of a coiled iilament 1 which is covered by a suitable insulating layer 2 and is disposed inside of the tubular member 3. The current source may be connected to the filaments in any suitable and desired manner, and of course any desired and suitable switching means may be disposed in the circuit. lt is assumed that in a cathode of this type, when constructed in accordance with known practice, the reduction or vaporization velocity of the emissive material at the operating temperature of the emitting surface is insufcient so that a deficiency of emissive material would result on such surface. Care is therefore taken to provide for an increased temperature for the emissive material. The heater comprising the lament 1 and the insulating layer 2 is for this purpose disposed in good heat transfer position relative to the emissive material 4. Less heat will be transferred to the emitting surface formed by the tightly wound tungsten or molybdenum wire 6. Suitable means, for example, 'a wire coil 5, is provided for spacing the body forming the emitting surface from the emissive material 4. The tightly wound coil of tungsten or molybdenum wire 6 form the very ne passages for the migration of the emissive material.

The at cathode illustrated in Fig. 2 comprises a body 8 which forms the emitting surface and overlies the receptacle 9 containing the supply of the emissive material 7. The body 8 may be a porous sintered material, for'example, sintered tungsten or molybdenum, or another suitable material which permits the migration of the emissive material. The receptacle 9 has an extended wall which is suitably secured to the sintered body 8, for example, by welding or soldering. Numeral 10 is a supporting member which is welded to the extension of the wall of the receptacle 9. Near the welding levels are disposed the windings 11 of the heater filament so as to transfer heat primarily to the sintered body 8 which forms the emitting surface. The receptacle 9 containing the emissive material 7 is relatively widely spaced from the heater 11, thus receiving less heat, thereby avoiding undesirable increase of the reduction or vaporization velocity, which would produce a wasteful excess of emissive material upon the cathode surface. A perforated intermediate plate 12 retains the emissive material 7 within the receptacle 9 to prevent spilling thereof in case of positional changes of the tube in which the structure is used. The emissive material escapes in the direction of the arrows 13. As in the structure described in connection with Fig. l, there is of course a suitable current supply for the heater 11 with such switching means as may be desired to regulate the heating thereof. This is also true in each and every one of the remaining embodiments.

The remaining embodiments are concerned with structures in which the reduction or vaporization velocity would be slow, if such structures were made in accordance with known principles, entailing the danger of insutiicient coverage of the emitting surface. In accordance with the invention, these embodiments therefore provide for auxiliary heating of the emissive material. i

Fig. 3 is a flat disklike cathode. The disk need not be l parallel.

circular; it may receive another form, for example, rectangular or narrow elongated form. This is also true With respect to the structure indicated in Fig. 2. rIhe emissive material 14 is disposed within a receptacle 16 which is covered by the body I5 forming the emitting surface. The latter may be sintered tungsten orv molybdenum or another suitable material which permits the migration of the emissive material. Numeral 17 indicates a supporting member which is at 18 suitably secured, for example, by welding, soldering or the like, to the receptacle 16 and to the sintered body 15. T Wo separate heaters are provided, one in the form of a at spiral 19 primarily for the heating of the emissive material 14, and another heater 20 in the form of a coil which is primarily elective to heat the body 15 forming the emitting surface.

The cathode illustrated in Fig. 4 is a tubular cathode shown in sectional View'.V The emissive material 21 is covered by a tungsten or molybdenum wire 22 which is tightly wound around a plurality of axially extending rods or wires 23. These rods or wires serve for the heating and are connected to a suitable current source in The cathode surface is thus heated directly, or partly directly and partly indirectly. In addition, there' is disposed another hea-ting coil 25 inside of the tubular member 24, which forms the inside retainer wall for the emissive material 21.

The structure shown in Fig 5 is a tubular cathode in which the emissive material' 26 is additionally heated by a centrally axially extending heater 27. The emissive material is covered by the body 28, which may be a porous sintered body as previously described. This body forms at its opposite ends anges 29 and 30, to provide for good heat transfer from the two heaters 31 and '32. Numeral 33 indicates the receptacle for the emissive material 26. This receptacle may be welded or otherwise suitably secured to the iianges 29 and 30 of the sintered body 2S. The heater spirals 31 and 32 provide, in connection with anges 29 and 30, for favorable heat transfer and therefore strong heating of the emitting surface formed by the sintered body 28. The required reducation or vaporization velocity of the emissive material may be regulated by the heater 27, which may be made to provide for a relatively mild heating effect.

The heating circuit for the heaters shown in Fig. 4 may be separate and may contain separate and independently regulable switching means along the line of elements shown in Figs. 3 and 5. If desired, suitable means, for example, suitable dielectrics, may be disposed between the heaters and their associated structures. The discharge device, in which a cathode may be used, comprises of course an envelope and other structures which have not been illustrated in the drawings, because they form no part of the invention.

Changes may be made within the scope and spirit of the appended claims.

We claim:

1. A dispenser type cathode comprising a body forming an emitting surface, wall means connected with said body and forming therewith a receptacle containing an emissive material, a first heating element disposed adjacent a portion of saidv wall means for transferring heat thereto so as to heat primarily said emissive material toV cause vaporizavtion and consequent migration thereof through said body to the emitting surface formed thereby, and a second heatingy element disposed in the vicinity of a portion of said body for separately transferring heat thereto to facilitate migration of said emissive material to said emitting surface.

2. A dispenser type cathode comprising a body forming an emitting surface, wall means connected with said body and forming therewith a receptacle containing an emissive material, a first heating element disposed directly adjacent a portion of said wall means for transferring heat thereto so as to heat' primarily said emissive material to causev vaporization and consequent migration thereof throughv said body to the emitting surface formed thereby, and a second heating element disposed directly adjacent a portion of said wall means which is connected with said body for separately transferring heat tov said body to facilitate migration of said emissive material to said emitting surface.

3. The structure dened in claim 1, wherein said body is a 'at disklike body forming a flat emittingv surface.

References Cited in the tile of this patent UNITED STATES PATENTS 1,701,356 Brickel et al. Feb. 5, 1929 2,071,973 Francis Feb. 23, 1937 2,121,589 Espe June 21, 1938 2,543,728- Lemmens et al. Feb. 27, 1951 

1. A DISPENSER TYPE CATHODE COMPRISING A BODY FORMING AN EMITTING SURFACE, WALL MEANS CONNECTED WITH SAID BODY AND FORMING THEREWITH A RECEPTACLE CONTAINING AN EMISSIVE MATERIAL, A FIRST HEATING ELEMENT DISPOSED ADJACENT A PORTION OF SAID WALL MEANS FOR TRANSFERRING HEAT THERETO SO AS TO HEAT PRIMARILY SAID EMMISIVE MATERIAL TO CAUSE VAPORIZATION TION AND CONSEQUENT MIGRATION THERETO THROUGH SAID BODY TO THE EMITTING SURFACE FORMED THEREBY, AND A SECOND 